[Grace-core] talking generics with Gilad over lunch

[Andrew P Black]

Remember our goal: a simple language for teaching, not so far out of the mainstream that it will scare the horses, I mean the instructors!

I think that this argues for wanting a special syntax for types that's ugly like other languages, just so that we can be ugly like other languages. But there is no reason that we can't translate that language into core Grace.

Types in Emerald were just objects — but objects with a particular signature.  There was a special syntax for creating such objects (the sub-language of types), and types created with this syntax were guaranteed to be decidable.   But you could, in principle, create other types out of whole cloth, and membership in such types might be undecidable.   This is quite like the idea that all Grace types are patterns, but not all patterns are types.

I think that we need to separate the researchy stuff on types from the simple language that we use for teaching.    If we can't do this, then we need to work more on the extension mechanisms.

	Andrew